This invention relates generally to engines, and more particularly to a variable valve actuation system for an engine.
An internal combustion engine typically includes a series of valves that are configured to control the intake and exhaust of gases to and from the engine. A typical engine will include at least one intake valve and at least one exhaust valve for each combustion chamber in the engine. The opening of each valve is typically timed to occur at a certain point in the operating cycle of the engine. For example, an intake valve may be opened when a piston is moving towards a bottom dead center position within a cylinder to allow fresh air to enter the combustion chamber. An exhaust valve may be opened when the piston is moving towards a top dead center position in the cylinder to expel exhaust gas from the combustion chamber.
The efficiency and emission generation characteristics of the engine may be improved by varying the actuation timing of the intake and/or exhaust valves to meet different engine operating conditions. For example, when the vehicle is reducing speed, the exhaust valve actuation timing may be varied to implement an xe2x80x9cengine brakingxe2x80x9d cycle. Engine braking involves opening the exhaust valves when the piston is approaching the top dead center position of a compression stroke to release compressed gas from the combustion chamber instead of inducing combustion. In this manner, the kinetic energy of the moving vehicle may be dissipated by compressing the gas in the compression chamber, which results in a slowing, or xe2x80x9cbraking,xe2x80x9d of the engine.
The actuation timing of the intake valves may also be varied to improve the performance of the engine when the engine is experiencing certain operating conditions. For example, a xe2x80x9clate intake Miller cyclexe2x80x9d may be implemented when the engine is experiencing steady state conditions. A late intake Miller cycle involves holding the intake valves open as the piston moves through an intake stroke and for a first portion of the compression stroke. The late intake Miller cycle may lead to improved engine efficiency and/or reduced emission generation.
To obtain these types of improvements in engine performance, the engine requires a valve actuation system that adjusts the valve actuation timing based on the current operating conditions of the engine. For example, when it is determined that the engine is operating in steady state conditions, the valve actuation system may vary the actuation timing of the intake valves to implement the late intake Miller cycle. Because the engine operating conditions may change frequently, the valve actuation system should be capable of quickly responding and varying the valve actuation timing to meet the current engine operating conditions.
Engine valves are typically actuated by either a cam driven system or a hydraulic system. In a conventional cam driven system, a cam having one or more cam lobes is rotated in conjunction with the engine crankshaft to actuate the engine valves. The shape of the cam lobes determines the valve actuation timing. This type of system is relatively inflexible as the timing of the engine valves will remain constant regardless of the vehicle operating conditions.
In a hydraulic system, a pressurized fluid is used to actuate the engine valves. A hydraulically driven system is typically more flexible than a cam driven system because the actuation timing of a hydraulic system is independent of crankshaft rotation. However, a hydraulic system typically requires additional components, such as a high pressure pump and a complex control system. These additional components may significantly increase the cost of the valve actuation system and the amount of maintenance required on the engine.
A valve actuation system may use a combination of cams and hydraulics that allow the valve actuation timing to be varied in response to different operating conditions. For example, the valve actuation system in U.S. Pat. No. 5,036,810 issued to Meneely on Aug. 6, 1991 combines a cam-driven rocker arm and a hydraulic system to effectuate engine braking. However, in this system the hydraulic components of the valve actuation system, including the passages supplying actuator fluid, are located above the rocker arm of the engine. This placement of the valve actuation components adds height to the engine. Therefore, such a system of valve actuation cannot be used on engines that have tight packaging constraints, such as light duty truck engines. In addition, systems with actuator fluid passages positioned above the rocker shaft often face problems in cold start conditions due to the viscosity of the actuator fluid. Because the actuator fluid is spaced from the heat-producing elements of the engine, in cold conditions the actuator fluid does not reach a satisfactory temperature in an appropriate time frame.
The engine valve actuation system of the present invention solves one or more of the problems set forth above.
An engine has a cylinder head having a first surface and a second surface spaced from the first surface. A valve is moveably connected to the cylinder head. A rocker arm is connected to the valve, and a rocker shaft having a first location spaced a maximum distance from the cylinder head is connected to the rocker arm. A support member has an actuator fluid passage network. The actuator fluid passage network defines a volume. The support member is positioned such that a majority of the volume of the actuator fluid passage network is between the first location of the rocker shaft and the second surface of the cylinder head.
A support member has a base. The base defines an actuator fluid passage network. The base is dimensioned to fit between a rocker shaft and a cylinder head of an engine.
An engine has a cylinder head having a first surface and a second surface spaced from the first surface. A valve is moveably connected to the cylinder head. A rocker arm is connected to the valve. The engine has a valve cover connected to the cylinder head. The valve cover has a first surface spaced no more than 3.5 inches (88.9) from the second surface of the cylinder head. A variable valve actuation means is connected to the rocker arm and is positioned between the second surface of the cylinder head and the first surface of the valve cover.
A method of assembling an engine includes providing an engine block and attaching a cylinder head to the engine block. The cylinder head has a first surface and a second surface spaced from the first surface. The method includes connecting a rocker shaft to a support member. The support member has an actuator fluid passage network. The actuator fluid passage network has a volume. The method includes connecting the variable valve actuation system to the cylinder head such that a majority of the volume of the actuator fluid passage network is located between the second surface of the cylinder head and a first location of the rocker shaft located a maximum distance from the cylinder head.